Strange issue with trailer brakes

I’m curious if there’s something I could’ve done as I’ve reported it to the company so they can repair or check it out.
So I picked up this trailer pretty new or refurb maybe (paint on the tandem lock is still sticky). I pull out of the dock and immediately the trailer brakes grab for a split second jerking me forward. I panic and think I dropped it or something and check everything out. No tread marks all wheels turning I physically look to make sure the brakes are released when the trailer air supply is pushed in.

Heading out I notice it keeps happening randomly at slow speeds. I get out and hear a hissing at the tandems and notice the secondary air pressure is falling. My yard was only 8 miles so I just limp it home. The issue stopped at above 45 mph or maybe I just stopped noticing it but I was listening and cruising slow to be safe. Then it started again when I got off the freeway.

Anyway any idea what could have caused this? Anything I could’ve done or checked?

 

Edit: the red knob never popped the compressor kept refilling the secondary only and it never dropped below 90 psi. It seemed to be more noticeable when making a turn. Or maybe it was just more noticeable then.